1. Field of the Invention
This invention generally relates to the development of a mining layout within a mineral deposit and more particularly to a means and method for developing single entries which provides for roof support and division of air paths without the use of multiple entry sets.
2. Description of the Prior Art
Conventionally, a mineral deposit to be mined is divided into sections by driving groups of entries into the body of the deposit following a designated pattern. The number of such entries in each group is determined by the requirements imposed by a number of factors, to wit, ventilation, escape ways, haulage, drainage, water supply and power supply. Usually in a mineral deposit with thicker overburden, the number of entries in each group is reduced. Three entries in each group is usually the minimum. Among the typical disadvantages of such a conventional mining development are: (1) high roof pressure occurs in lower levels (e.g., multi-seam coal mining), (2) high cost and long period of time for mine development, (3) low extraction ratio, (4) extensive openings have to be inspected and maintained, (5) often requires complicated ventilation system, (6) extensive surface exposure causes dust problem (very serious in coal mines), (7) chain pillars create burst environment (rock or coal burst), and (8) continuous miner and roof bolting equipment system often exposes workers under improperly supported roof.
Chain pillars separating adjacent entries in a conventional development inevitably produce pressure buildup which is particularly harmful when successive layers are to be mined. Furthermore, the chain pillar construction forces a so-called "continuous" loader to operate intermittently. This is because it has to back up and develop the "breaks" between pillars, and stoppings have to be set up between each two of such pillars.
For the above reasons, single-entry mining of longwall underground mineral seams has been researched in this country. As an example, Kaiser Steel Corporation has been conducting a program of this type in operations at Sunnyside, Ut. This is reported in an article in the 1975 Mining Yearbook of the Colorado Mining Association beginning at page 101. The system described employs entries developed by a continuous miner and separated into two halves by fire retardant treated cribs installed not more than 4 feet apart along the entry's center line. Galvanized metal panels are attached to the cribs to form a curtain wall to establish intake and return entries, which are then sprayed to give an airtight seal and reduce the thermal gradients between sides. A travel curtain for a shuttle car and line brattice are used to ventilate the face from the end of the cribs and curtain wall. The cribs and curtain wall are said to be installed within 150 feet of the face at all times.
The advance rate of a single entry of the type described is necessarily limited by the speed and efficiency with which the entry dividing means can be erected. It is therefore with these problems that the present invention is most immediately concerned.